Any good classes or libraries for quaternion's?

I found one at Perone’s Programming pad, but I am having difficulty in using it because there is no documentation. What do you all use?

I’m using OpenTK.Math’s quaternions.
Even if you are not under .NET, you can take a look at OpenTK sources.

Thanks for the suggestion, but I found this:

Some other alternatives …

A good book that uses quaternions and has source code is “Physics for Game Developers” by David Bourg (see the link to Crash Test example for the mymath.h file ). This book helped me learn about the use of quaternions and application to physics sims – they regretfully don’t use openGL or my linux OS (but the other OS). However it is still a good explanation of the application of quaternions to physics computations.

Lately, I have been using the GLM OpenGL math Library because it matches the notation of openGL GLSL and it has quaternions as an extension. The documentation is sparse but it has been working very well for my transition to OpenGL 3.2.